A convenient protocol for selective cleavage of 2-hydroxy acid amides. Application to semisynthesis of the cyclic heptapeptide aza HUN-7293

J Org Chem. 2002 Nov 29;67(24):8299-304. doi: 10.1021/jo025979g.

Abstract

A two-step protocol for the first chemoselective cleavage of 2-hydroxy acid amides has been developed. Mesylation of the model substrate 2-(hydroxypropionylamino)-4-methylpentanoic acid methyl ester (11) followed by treatment with N-ethylthiourea (13) allows cleavage of 2-hydroxy acid amides under smooth conditions. Successful application of this methodology to the open-chain transesterification product 15 (methylester) of the cyclic heptadepsipeptide HUN-7293, a potent inhibitor of inducible cell adhesion molecule expression, delivered the corresponding hexapeptide 18 with unprotected N-terminus in 70-75% yield. This result demonstrates that the protocol developed even works in the presence of an ester and several methylated and unmethylated amide bonds. Finally, a sequence of ligation of methyl D-dehydroglutaminate (20) to the C-terminus of the saponification product 21, followed by the degradation protocol and ring closure, allowed chemical "point mutation" at the DGCN site affording the aza analogue of HUN-7293 (24) in 15% overall yield. To the best of our knowledge this is the first report on chemoselective cleavage of 2-hydroxy acid amides.

Publication types

  • Comparative Study

MeSH terms

  • Amides / chemistry*
  • Amino Acid Sequence
  • Catalysis
  • Cell Adhesion / drug effects
  • Combinatorial Chemistry Techniques*
  • Cyclization
  • Hydroxy Acids / chemistry*
  • Magnetic Resonance Spectroscopy
  • Methylation
  • Models, Molecular
  • Molecular Structure
  • Peptides, Cyclic / analysis
  • Peptides, Cyclic / chemical synthesis*
  • Structure-Activity Relationship

Substances

  • Amides
  • HUN 7293
  • Hydroxy Acids
  • Peptides, Cyclic